Comparison of in-plane shear behaviors of 2-d plain woven C/SIC composites

The in-plane shear behavior of a plain woven C/SiC composite which exhibits typical ductile tensile behavior (failure strain 0.6-0.8 %) was investigated and compared with that of a brittle plain woven C/SiC composite (tensile failure strain 0.05 %). The shear behavior of ductile composite can be characterized by an initial elastic regime below stress of 40-50 MPa, and a large nonlinear regime followed by a plateau regime up to final failure strain (>2 %), while only the first elastic and last plateau regime can be found for the brittle composite despite that similar shear strain-to-failure and shear knee stresses were found for both ductile and brittle composites. The critical shear stress for matrix cracking was found to be close to the proportional limit stress of ductile composites or strength of brittle ones under uniaxial tensile loading, which could be attributed to the same mechanism of matrix cracks due to the principal tensile stress. Longitudinal intra-yarn cracks and delamination were found for both composites, which could be predominantly responsible for the large shear failure strains observed.